Concerns about privacy are running so high that 60 per cent of the 1,588 Facebook users questioned by Sophos, a computer security organisation, said they were considering deleting their accounts on the social networking site.

A further 16 per cent said they had already stopped using Facebook because they felt they had inadequate control over their data, while a quarter said that they would not be quitting the social networking site, which has almost 500 million users worldwide.

Facebook has attracted criticism in recent weeks for the perceived complexity of its privacy settings, and the fact that users have to opt-out of sharing some of their information with third parties, rather than give explicit consent by opting in. Although Facebook is expected to look again at its privacy policy in the coming days, it may not be enough to halt an online campaign for a mass Facebook "suicide" on May 31, with thousands of users encouraged to delete their accounts.

"This poll shows that the majority of users are fed up with the lack of control that Facebook gives users over their data," said Graham Cluley, senior technology consultant at Sophos. "Most still don't know how to set their Facebook privacy options safely, finding the whole system confusing. What's needed is a fundamental shift towards asking users to 'opt-in' to sharing information, rather than to 'opt-out'.

"A mass exodus from Facebook seems unlikely, but users are clearly getting more interested in knowing precisely who can view their data. People use Facebook to share private information and are unlikely to want their holiday snaps or new mobile number accidentally popping up all over the internet."